TECHNICAL FIELD
[0001] The present invention relates to improvement in tracer control equipment, and more
particularly to tracer control equipment which enables deceleration control at a jerk
point in the configuration of a model to be optimum to the configuration of thereof
at that particular point.
BACKGROUND ART
[0002] In the case of tracing a model M of such a configuration as shown in Fig. 4, if the
jerk points (a) to (c) in the configuration of the model are traced at the same speed
as that for flat surfaces of the model, a cutter can bite into a workpiece at the
jerk point (a) and a stylus ST can move out of contact with the surface of the model
M at the jerk points (b) and (c). To avoid this, it is a general practice in the prior
art to compare the variation of a displacement signal from a tracer head per unit
time with a preset value and reduce the feed rate to a predetermined value while the
former is greater than the latter. That is, since the displacement signal from the
tracer head undergoes an abrupt change at each jerk point in the configuration of
the model and the variation of the displacement signal per unit time also varies abruptly
at the jerk point, it is possible to prevent the biting of the cutter into the workpiece
and other similar trouble by controlling the feed rate as mentioned above.
[0003] According to the above-mentioned prior art example, however, when the changing ratio
of the displacement signal exceeds a predetermined value, the feed rate is reduced
to a predetermined value regardless of the configuration of the model at the jerk
point; so that it is impossible to perform optimum deceleration control corresponding
to the configuration of the model at the jerk point. Namely, according to the prior
art example, the feed rate during deceleration must be set low so that the cutter
will not bite into the workpiece even when the stylus traces a sharp corner of the
model. Consequently, when deceleration control takes place at a gentle corner portion,
the feed rate undergoes an abrupt change, which results in the problem of deterioration
of the workpiece surface.
DISCLOSURE OF THE INVENTION
[0004] The present invention has overcome the defect mentioned above, and has as an object
enabling optimum deceleration control corresponding to the configuration of the model
at a jerk point therein.
[0005] To solve the above-noted problem, the tracer control equipment of the present invention,
which controls the relative feed rate between the model and the tracer head tracing
the surface thereof, in accordance with the displacement signal from the latter, is
provided with detecting means for detecting the variation of the displacement signal
per unit time, decision means for comparing the detected variation of the displacement
signal with a plurality of threshold values of different levels and deciding which
of regions defined by the thershold values the variation of the displacement signal
belongs to, and deceleration control means whereby the relative feed rate between
the tracer head and the model is reduced to and held at a value corresponding to the
result of the decision by the decision means during a period from the time when the
variation of the displacement signal is decided by the decision means to have exceeded
the threshold value of a level lower the lowest level than those of the other threshold
values to the time when it is decided to have returned to a value smaller than the
threshold value of the lowest level.
[0006] According to the tracer control equipment of the present invention, since the feed
rate for deceleration control is determined depending upon which of the regions defined
by the plurality of threshold values the variation of the displacement signal per
unit time belongs to, optimum deceleration control can be achieved corresponding to
the configuration of the model at the jerk point. Furthermore, since the deceleration
control means continues its deceleration control until the variation of the displacement
signal becomes smaller than the threshold value of the lowest level again after having
exceeded it, deceleration and its removal will not be repeated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007]
Fig. 1 is a block diagram of an embodiment of the present invention; Fig. 2 is a block
diagram illustrating an example of the arrangement of a deceleration control circuit
18; Fig. 3 is a diagram for explaining the operation of the circuit shown in Fig.
3; and Fig. 4 is a diagram for explaining a defect of a prior art example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0008] Fig. 1 illustrates in block form an embodiment of the present invention. Reference
numeral 1 indicates a tracer head, 2 a stylus, 3 a composite displacement signal generator,
4 an adder, 5 and 6 velocity calculation circuits, 7 a distribution circuit, 8 a gate
circuit, 9 a change-over circuit, 10 an indexing circuit, 11X, 11Y and 11Z amplifiers
in the X, Y and Z axes, 12X, 12Y and 12Z motors in the X, Y and Z axes, 13 a microprocessor,
14 a memory, 15 an output port, 16 and 17 DA converters, and 18 a deceleration control
circuit.
[0009] The tracer head 1 outputs displacement signals ε
X, ε
Y and ε
z corresponding to the displacement of the stylus 2 in the X-, Y- and Z-axis directions
which moves in contact with a model. The displacement signals ε
x, ε
Y and ε
z are provided to the composite displacement signal generator 3, the change-over circuit
9, and the deceleration control circuit 18. The composite displacement signal generator
3 yields a composite displacement signal, ε = ν ε
x2 + ε
y2 + ε
z2, which is applied to the adder 4. The adder 4 obtains a differnce, Δε
= c - ε
0, between the composite displacement signal e and a reference displacement signal
ε
0 which is provided via the output port 15 and the DA converter 16. The difference
Ae thus obtained is applied to the velocity calculation circuits 5 and 6. Based on
the difference Δε, the velocity calculation circuits 5 and 6 obtain a normal-direction
velocity signal V
N and a tangential-direction velocity signal V
T, which are provided to the distribution circuit 7. The change-over circuit 9 supplies
the indexing circuit 10 with that one of the displacement signals ε
X, ey and ε
Z from the tracer head 1 which corresponds to the axis constituting the plane being
traced. The indexing circuit 10 produces displacement-direction signals sine and cosθ
on the basis of the displacement signals which are applied via the change-over circuit
9. Incidentally, when the plane of tracing is the X-Z plane, the X- and Z-axis displacement
signals ε
x and ε
z are provided via the change-over circuit 9 to the indexing circuit 10.
[0010] The distribution circuit 7 generates a velocity command signal, based on the normal-direction
and tangential-direction velocity signals V
N and V
T from the velocity calculation circuits 5 and 6 and the displacement-direction signals
sinθ and cos6 from the indexing circuit 10. The velocity command signals is applied
to the amplifier selected by the gate circuit 8 , and the resulting amplified output
drives the corresponding motor, feeding the tracer head 1 and the model relative to
each other. Since the above-described operation is well-known as tracer control, no
further detailed description thereof will be given.
[0011] Fig. 2 illustrates in block form an example of the arrangement of the deceleration
control circuit 18 which controls the feed rate in accordance with the configuration
of the model. Reference numerals 21 to 23 designate differentiation circuits, 24 an
arithmetic circuit, 25 to 27 comparators, 28 to 30 rise detectors, 31 to 33 fall detectors,
34 and 35 counters, 36 a comparator, 37 a zero detector, 38 an attenuator, 39 an acceleration/deceleration
circuit, 40 a coincidence detector, 41 a comparator, OR1 and OR2 OR gates, and AND
an AND gate.
[0012] The differentiation circuits 21 to 23 in the deceleration control circuit 18 differentiate
the displacement signals ε
X, Cy and ε
Z which are applied thereto from the tracer head 1, the differentiated outputs being
provided to the arithmetic circuit 24. The arithmetic circuit 24 produces a signal,
ε'=√ε
X'
2 +
Ey'
2 + ε
Z'
2, based on the output signals ε
X', ε
Y' and ε
Z' from the differentiation circuits 21 to 23. The comparators 25 to 27 compare the
output signal e' from the arithmetic circuit 24 with predetermined threshold values
Ll, L2 and L3 (where Ll < L2 <L3), respectively, and make their output signals a,
b and c "ls" while the output signal c' from the arithmetic circuit 24 is greater
than the threshold values. The rise detectors 28 to 30 make their output signals "ls"
for only a predetermined period of time T at the rise of the output signals a to c
from the comparators 25 to 27, respec- tivley. The fall detectors 31 to 33 make their
output signals "ls" for only the predetermined period of time T at the fall of the
output signals a to c from the comparators 25 to 27, respectively.
[0013] The counter 34 increments its count value CA by one each time the output signal d
of the OR gate OR1 which ORs the output signals from the rise detectors 28 to 30 goes
to a "1", and it is reset when the output signal i of the AND gate AND goes to a "1";
namely, its count value CA is made a "0". The counter 35 increments its count value
CB by one each time the output signal d of the OR gate OR1 which is applied to its
+ terminal goes to a "1", and it decrements its count value CB by one each time the
output signal e of the OR gate OR2 which is applied to its - terminal goes to a "1".
The comparator 36 compares the count values CA and CB of the counters 34 and 35 and
makes its output singal f a "1" when the condition CA > CB is satisfied. The zero
detector 37 makes its output signal g a "1" when the count value CB of the counter
35 is a "0".
[0014] The attenuator 38 attenuates a velocity command signal Vcmd which is provided thereto
via the DA converter 17 from the microprocessor 13, with an attenuation factor corresponding
to the count value CA of the counter 34 (which attenuation factor is zero when the
count value is a "0", and increases as the count value CA increases). The acceleration/deceleration
circuit 39 operates as a filter with a time constant
T1 when the output signal k of the comparator 41 is a "1" and, as a filter with a time
constant
T2 (where
T2 » τ
1) when the output signal k is a "0", the output signal Vb being applied to the velocity
calculation circuit 6. The comparator 41 compares the output signal Va of the attenuator
38 and the output signal Vb of the acceleration/deceleration circuit 39 and makes
its output signal k a "1" while Vb > Va. Accordingly, the acceleration/deceleration
circuit 39 operates as the filter with the time constant τ
1 during deceleration and as the filter with the time constant τ
2 durint tracing at the normal feed rate. The coincidence detector 40 makes its output
signal h a "1" when detecting coincidence between the output signal Va of the attenuator
38 and the output signal Vb of the acceleration/deceleration circuit 39. The velocity
calculation circuit 6 varies its input/output characteristic in accordance with the
level of the output signal Vb from the acceleration/deceleration circuit 39 in such
a manner that the lower the level of the signal Vb becomes, the more the output level
(the tangential-direction velocity signal V
T) for the same input level is lowered.
[0015] Accordingly, assuming that the stylus has reached a jerk point in the configuration
of the model, for example, at a time tl, the output sitnal
E' of the arithmetic circuit 24 abruptly rises in level at the time tl, as shown in
Fig. 3(A). In response to this, the output signals a to c of the comparators 25 to
27 go to "ls" in succession, as depicted in Figs. 3(B) to (D), with the result that
the output signal d of the OR gate OR1 which ORs the output signals of the rise detectors
28 to 30 goes to a "1" at the rise of each of the signals a to c, as shown in Fig.
3(E).
[0016] As the output signal d of the OR gate OR1 undergoes such variations as depicted in
Fig. 3(E), the count values CA and CB of the counters 34 and 35 are gradually incremented
in the order "0", "1", ... , as shown in Figs. 3(G) and (H), respectively. The increase
in the count value CA of the counter 34 increases the attenuation factor of the attenuator
38, and consequently its output signal Va diminishes stepwise, as indicated by the
solid line in Fig. 3(K). At the same time, the output signal Vb of the acceleration/deceleration
circuit 39 also gradually diminishes from the level Vcmd, with the time constant
T1, as indicated by the broken line in Fig. 3(K).
[0017] As a result of this, the level of the tangential-direction velocity signal V
T' which is provided from the velocity calculation circuit 6, drops in proportion to
the decrease in the level of the output signal Vb of the acceleration/deceleration
circuit 39, thus decreasing the feed rate.
[0018] Then, when the output signal e' of the arithmetic circuit 24 diminishes, the output
signals c, b and a of the comparators 27, 26 and 25 go to "Os" in succession, as depicted
in Figs. 3(D), (C) and (B), respectively. In consequence, the output signal e of the
OR gate OR2, which ORs the output signals of the fall detectors 31 to 33, goes to
a "1" at the rise of each of the signals c to a, as shown in Fig. 3(F). As the output
signal e of the OR gate OR2 varies, as shown in Fig. 3(F), the count value CB of the
counter 35 gradually decreases, as depicted in Fig. 3(H). When the count value CB
has reached "2", the output f of the comparator 36 goes to a "1", as depicted in Fig.
3(1), and when the count value CB has reached "0" (at a time t2), the output signal
g of the zero detector 37 goes to a "1", as shown in Fig. 3(J).
[0019] When the output signal g of the zero detector 37 has thus risen to the "1" level
at the time t2, the output signal i of the AND gate AND, by which are ANDed the output
signal f of the comparator 36, the output signal g of the zero detector 37, and the
output signal h of the coincidence detector 40, shown in Figs. 3(1), (J) and (L),
respectively, goes to a "1", as depicted in Fig. 3(M). The output signal i resets
the counter 34 to make its count value CA a "0", in consequence of which the attenuation
factor of the attenuator 38 is reduced to zero and its output signal Va assumes the
level Vcmd, as indicated by the solid line in Fig. 3(K). Furthermore, the increase
in the level of the output signal Va of the attenuator 38 causes an increase in the
level of the output signal Vb of the acceleration/deceleration circuit 39, as indicated
by the broken line in Fig. 3(K). In this case, however, since Va > Vb and the output
signal k of the comparator 41 remains at the "0" level, the signal Va gradually increases
with the time constant
T2.
[0020] Then, as the level of the output signal Vb of the acceleration/deceleration circuit
39 rises, the level of the tangential-direction velocity signal V
T from the velocity calculation circuit 6 rises, ceasing deceleration control.
[0021] As described above, according to this embodiment, since the output signal e' of the
airthmetic circuit 24 is compared with the plurality of threshold values Ll to L3
(where Ll < L2 < L3) and the feed rate is reduced to a value corresponding to the
level of the signal
E', it is possible to perform optimum deceleration control corresponding to the configuration
of the model at a jerk point therein. Moreover, once the signal ε' exceeds the threshold
value L, the deceleration control is continued until the signal ε' returns to the
threshold value Ll, and consequently deceleration and its removal will not be repeated
during deceleration control.
[0022] While in the above embodiment the threshold values are described to be three, i.e.
Ll to L3, they are not limited specifically thereto as long as they are plural.
[0023] As described above, the present invention is provided with detecting means (which
comprises the differention circuits 21 to 23 and the arithmetic circuit 24 in the
embodiment) for detecting the variation of a displacement signal from the tracer head
per unit time, decision means (which comprises the comparators 25 to 27 in the embodiment)
for comparing the detected variation of the displacement signal and a plurality of
threshold values of different levels and deciding which of regions defined by the
threshold values the detected variation of the displacement signal belongs to, and
deceleration control circuit (which comprises the rise and fall detectors 28 to 33,
the OR gates OR1 and OR2, the counters 34 and 35, the comparator 36, the zero detector
37, the AND gate AND, and the attenuator 38) whereby the relative feed rate between
the tracer head and a model is reduced to and held at a value corresponding to the
result of decision by the decision means during a period from the time when the variation
of the displacement signal is decided by the decision means to have exceeded the threshold
value of a level lower than those of the other threshold values to the time when it
is decided to have returned to a value smaller than the threshold value of the lowest
level. Since the feed rate during deceleration can be changed in accordance with the
variation of the displacement signal per unit time, that is, according to the configuration
of the model at a jerk point therein, the present invention possesses the advantage
that optimum deceleration control can be effected in accordance with the configuration
of the model at the jerk point. Furthermore, since the deceleration control means
continues deceleration control over the entire period from the time when the variation
of the displacement signal exceeds the threshold value of a level lower than those
of the other threshold values to the time when it returns to a value smaller than
the threshold value of the lowest level, the present invention has another advantage
that deceleration and its removal will not be repeated during deceleration control.